Stretch marks or something else?

Ellie
Hi, sorry this is long but please read and comment if you can shed some light on the situation :)
So over the last year I have gone from a UK8 to a UK10 on my lower half.
 I hasn't really bothered me that I have put on weight until about 6 months ago when I started noticing these pink marks on my legs. 
I have had stretch marks before, just a few on my hips but they were skin coloured, never changed and it literally looked like the skin was stretched a tad. 
Now, the marks below can get very red sometimes and are all over the inside and backs of my legs and working towards my hips. Heat seems to make a difference as to how pronounced they are. 
Has anyone else had this? Are they stretch marks or something else? Thought I'd ask on here before seeing a doctor as they don't affect me in a physical way, just cosmetic/aesthetic. 
Thanks! X